1. Field of the Invention
The present invention relates generally to the field of semiconductor manufacturing. More specifically, the present invention relates to a method of achieving low contact resistance and to improving titanium nitride barrier performance for copper integration.
2. Description of the Related Art
With the down-scaling and increased speed of semiconductor devices being fabricated currently and with the levels of integration in VLSI and ULSI integrated chips, metallization processes require low resistance metals. Traditionally, aluminum has been used for interconnects in semiconductor devices, but recently, copper, with its lower resistance and better electromigration lifetime than that of aluminum, has been used for integration. However, copper is very mobile in many of the materials used to fabricate semiconductor devices. Copper can diffuse quickly through certain materials including dielectrics such as oxides. This causes damage to nearby devices on the semiconductor substrate. Thus, it is necessary to have copper barrier layers in place to avoid any copper diffusion within the semiconductor device.
Titanium nitride layers can serve as barrier layers against diffusion, including copper diffusion, in semiconductor device structures, e.g., contacts, vias and trenches. Deposition of an effective and useable titanium nitride barrier layer realizes good step coverage, sufficient barrier thickness at the bottom of device features and a conformal film having a smooth surface for further processing steps. However the TiN barrier layer must be as thin as possible to accommodate the higher aspect ratios of today's devices. Additionally, the TiN barrier layer must be inert and must not adversely react with adjacent materials during subsequent thermal cycles, must prevent the diffusion or migration of adjacent materials through it, and must have low resistivity (exhibit high conductivity), low contact or via resistance and low junction leakage.
Titanium nitride layers can be deposited on a wafer by the rapid thermal nitridation of a titanium layer or by any deposition process, e.g., sputtering (PVD) and CVD. CVD deposition of titanium nitride barrier films eliminates the problems with metal reliability and junction leakage associated with PVD deposited TiN barrier films and is considered a cleaner process than PVD TiN. Additionally, the CVD process produces conformal films with good step coverage in the 0.35 micron or less structures found in state of the art VLSI and ULSI devices. In a CVD process a metalorganic precursor such as tetrakisdimethylamino titanium (TDMAT) or tetrakisdiethylamino titanium (TDEAT) is thermally decomposed to deposit a titanium nitride layer.
However, MO CVD TiN does not provide good barrier performance to copper diffusion compared to, for example, IMP tantalum or IMP tantalum nitride. This film contains carbon and is a porous film that easily absorbs oxygen thereby becoming highly resistive and unstable. It is critical to have an effective barrier with copper metallization. Electromigration of copper into the silicon substrate ruins device performance.
Barrier performance of a TiN film can be improved by altering the method of deposition and/or the components of the film. Titanium nitride sputtered by using high density plasma techniques, such as those where a relatively large proportion of the material sputtered from the target is ionized and electrically attracted to the substrate, has produced smooth conformal films with low resistivity for subsequent aluminum deposition thereon. Titanium-silicon-nitrogen compounds provide a better diffusion barrier for aluminum or copper interconnects than titanium nitride barriers. Silane is used to incorporate silicon into a MOCVD TiN film in such a manner that a silicon rich surface is formed on the titanium nitride. This method does not utilize an in situ plasma step to further improve the film properties of the titianium nitride layer and the silicon is primarily deposited on the surface of the underlying titanium nitride layer.
Additionally, a high temperature method to deposit a porous titanium nitride layer with subsequent exposure firstly to a silicon-containing gas ambient and secondly to a low plasma power generated N2/H2 plasma incorporates silicon, as silicon nitride, primarily on the surface of the titanium nitride film. However, lower wafer temperatures are desired, as previously deposited material may have critical heat and temperature limitations. For example, current generation low k dielectric materials require wafer temperatures below approximately <380-400° C. Also, higher rf power can provide for efficient film treatment realizing low film resistivity and via resistance and providing for faster throughput. Thus, there exists a need in the art to further improve the barrier performance of titanium films for subsequent copper integration.
Therefore, a need exists for an improved effective means of improving titanium nitride barrier performance for copper integration. Specifically, there is a lack of effective means of incorporating silicon as silicon nitride into a titanium nitride layer thereby improving barrier performance for copper integration. The present invention fulfills these long-standing needs and desires in the art.